A semiconductor device has been proposed that includes a junction barrier Schottky diode structure. In the junction barrier Schottky diode structure, a Schottky barrier diode section and a p-n diode section are arranged adjacent to each other.
In this type of semiconductor device, under reverse bias, a depletion layer formed at a p-n diode section extends to a Schottky barrier diode section so that a reduction in leak current and an increase in surge strength can be achieved. Further, under forward bias, a low on-resistance and a fast reverse recovery time can be achieved by the Schottky barrier diode section.
US 2002/0125482 corresponding to JP-A-2003-510817 discloses a semiconductor device that includes a junction barrier Schottky diode structure. The semiconductor device includes an n-type semiconductor substrate having a p-type semiconductor region exposed to its top surface. An electrode made of an alloy of nickel and aluminum is formed on the top surface of the semiconductor substrate. The electrode is in Schottky contact with an n-type semiconductor region exposed to the top surface. of the semiconductor substrate. Further, the electrode is in ohmic contact with the p-type semiconductor region exposed to the top surface of the semiconductor substrate.
U.S. Pat. No. 7,274,083 also discloses a semiconductor device that includes a junction barrier Schottky diode structure. The semiconductor device includes an n-type semiconductor substrate having a p-type semiconductor region on its top surface. The p-type semiconductor region has a mesa structure. A Schottky electrode and an ohmic electrode are individually formed on the top surface of the semiconductor substrate. The Schottky electrode is in Schottky contact with an n-type semiconductor region exposed to the top surface of the semiconductor substrate. The ohmic electrode is in ohmic contact with the p-type semiconductor region exposed to the top surface of the semiconductor substrate.
In the semiconductor device disclosed in US 2002/0125482, a portion of the electrode in Schottky contact with the n-type semiconductor region of the semiconductor substrate and a portion of the electrode in ohmic contact with the p-type semiconductor region of the semiconductor substrate are made of the same kind of a material. Therefore, it may be difficult for the electrode to satisfy both characteristics required for a Schottky electrode and characteristics required for an ohmic electrode.
In the semiconductor device disclosed in U.S. Pat. No. 7,274,083, the Schottky electrode and the ohmic electrode are individually formed. Specifically, the Schottky electrode is formed, after the ohmic electrode is formed. In this case, there is a possibility that a material used to form the ohmic electrode remains left on the surface of the semiconductor substrate, when the Schottky electrode is formed on the surface. If a foreign matter is interposed between the semiconductor substrate and the Schottky electrode, a Schottky contact between the semiconductor substrate and the Schottky electrode changes greatly. The change in the Schottky contact may cause problems such as an increase in leak current.